As an example, there is a shear mode piezoelectric actuator for use in an inkjet head. This has the structure as shown in FIG. 11 in which a plurality of wall parts 22 made of a piezoelectric material formed in a comb teeth shape on a substrate 21, rectangular ink chambers 23 adjacently formed between the wall parts, and the wall parts 22 deformed to vary the volume of the ink chambers for discharge operation.
Such an actuator is formed by the steps shown in FIG. 7. First, a piezoelectric material 17 is prepared in FIG. 7A, and is fired in FIG. 7B. After being fired, the piezoelectric material is polarized in FIG. 7C. Then the fine slits are formed by a dicing saw or the like to form driving portions 18 in a comb teeth shape, and a plurality of slits 19 for storing ink are formed and arranged in FIG. 7D. Then electrodes 20 are formed on the wall surfaces inside the slits in FIG. 7E. After that, as shown in FIG. 11, the ink chambers are closed with a cover plate 24 made of a glass plate or the like, and the opening parts at the tip ends are closed with a nozzle plate 25 formed with nozzles 26.
However, in the manufacturing method described above, the corner parts tend to be chipped because a hard plate made of piezoelectric material is machined, having the following problems.
Firstly, it takes time for slit machining, as such it is unsuitable for mass production.
Secondly, a sufficient cleaning to drying process is needed because the actuator is contaminated with free abrasive grains from machining or working fluids used after slit machining. However, a complex and expensive cleaning process is required for satisfactory cleaning because the parts are weakened by the slit machining.
Thirdly, the width of slits, being used as ink chambers, is limited by the dicer blade to a width of about 70 μm or less. A determination of the width limit must consider the depth of the slits because the wall must be sufficiently thick to withstand the force of the dicer blade making a cut. With this requirement, it is difficult to form at an aspect ratio of 10 or more. On this account, it is impossible to obtain a comb-tooth type actuator of high density, or of high strength and high power output.
Fourthly, only linearly, flat slit machining can be performed because machining is performed by the dicer blade, and components are bonded or the like in downstream process in response to a complex form. As the result of linear machining, piezoelectric stress deformation is generated up to the end of the joined nozzle plate during actuation, causing the durability of the joined surfaces to be reduced.
Fifthly, since the slits are formed by cutting, transgranular fracture is generated in crystal grains located in the side surfaces of the comb teeth, likely causing deterioration in the mechanical properties due to residual compressive stress. FIG. 8 is an explanatory drawing illustrating this. FIG. 8A is an end view as seen from Q shown in FIG. 7, and FIG. 8B is an enlarged sectional view of area N, from FIG. 8A. Piezoelectric crystal grains in the surface of the comb tooth are indicated by slant lines. A part thereof is chipped by cutting with the dicing saw, which generates transgranular fractures, causing deterioration in the mechanical properties. In addition, micro-cracks often occur between the crystal grains or inside the grains by cutting, sometimes causing deterioration in the mechanical properties.